Dubbo使用指南

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Dubbo介绍

简单的来说，Dubbo是一个服务治理的框架，集中管理了RPC调用，并提供多种访问策略和负载来满足应用系统之间的相互调用。

Dubbo架构

Provider: 暴露服务的服务提供方。
Consumer: 调用远程服务的服务消费方。
Registry: 服务注册与发现的注册中心。
Monitor: 统计服务的调用次调和调用时间的监控中心。
Container: 服务运行容器。

注意：Registry是一个很轻的东西，实际上Dubbo只是在注册中心共享了服务的相关信息，Dubbo的主体是Provider和Consumer，这两者都是属于应用范围内的。Monitor也是很轻的模块，需要有监控服务在Registry进行了注册应用才能正常使用监控，监控宕掉不影响服务。

协议介绍

Dubbo本身提供了多种协议的支持，我们系统内广泛使用的hession协议也是其中之一。

dubbo://
Dubbo缺省协议采用单一长连接和NIO异步通讯，适合于小数据量大并发的服务调用，以及服务消费者机器数远大于服务提供者机器数的情况。
Dubbo缺省协议不适合传送大数据量的服务，比如传文件，传视频等，除非请求量很低。
rmi://
RMI协议采用JDK标准的java.rmi.*实现，采用阻塞式短连接和JDK标准序列化方式。
hessian://
Hessian协议用于集成Hessian的服务，Hessian底层采用Http通讯，采用Servlet暴露服务，Dubbo缺省内嵌Jetty作为服务器实现。
http://
基于http的短连接协议，基本不会去使用了。
webservice://
webservice
redis://
Redis是一个高效的KV存储服务器
memcached://
Memcached是一个高效的KV缓存服务器
Thrift://
Thrift是Facebook捐给Apache的一个RPC框架

注册中心介绍

Dubbo也支持多种类型的注册中心，分别有：

Multicast
基于组播实现的注册中心，互相发现
Zookeeper
Zookeeper是Apacahe Hadoop的子项目，是一个树型的目录服务，支持变更推送，适合作为Dubbo服务的注册中心，工业强度较高，可用于生产环境，并推荐使用。
Redis
Redis是一个高效的KV存储服务器
Simple
注册中心本身就是一个普通的Dubbo服务，可以减少第三方依赖，使整体通讯方式一致。

完整介绍

目前我们系统使用的协议是Dubbo协议，注册中心是Zookeeper，这两者可以仔细去了解一下，下面给出Dubbo的官方文档地址：

User+Guide-zh

使用示例

下面我会给出一个完整的基于Dubbo服务的调用代码示例，需要注意的点我在注释上说明。

接口定义

定义Maven接口项目
pom.xml
<project xmlns="<a href="http://maven.apache.org/POM/4.0.0" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://maven.apache.org/POM/4.0.0" xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 <a href="http://maven.apache.org/xsd/maven-4.0.0.xsd" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.lefu</groupId>
  <artifactId>Iexample</artifactId>
  <version>1.0</version>
</project>
定义接口

ISayHello.java
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package com.lefu.iexample;
public interface ISayHello {
public String sayHelloWaitAnswer(String s);
}

服务提供方(Provider)

定义Maven服务端项目，并提供相应依赖(Iexample,dubbo,zookeeper)。
pom.xml
<project xmlns="<a href="http://maven.apache.org/POM/4.0.0" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://maven.apache.org/POM/4.0.0" xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 <a href="http://maven.apache.org/xsd/maven-4.0.0.xsd" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.lefu</groupId>
  <artifactId>example-server</artifactId>
  <version>1.0</version>
  <dependencies>
    <dependency>
        <groupId>com.lefu</groupId>
        <artifactId>Iexample</artifactId>
        <version>1.0</version>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>dubbo</artifactId>
        <version>2.5.3</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>3.2.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>com.github.sgroschupf</groupId>
        <artifactId>zkclient</artifactId>
        <version>0.1</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.6.4</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.6.4</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.16</version>
    </dependency>
  </dependencies>
</project>
Dubbo对外的依赖是需要什么就增加什么的jar依赖，我们需要到的依赖一个是dubbo自身的依赖，另外一个是注册中心zookeeper的依赖，需要提供zookeeper的连接客户端，再者就是需要实现的接口jar了。
实现接口的服务类
SayHelloImpl.java
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package com.lefu.example.server.rpc;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.atomic.AtomicInteger;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.lefu.iexample.ISayHello;
public class SayHelloImpl implements ISayHello {
    private final Logger log = LoggerFactory.getLogger(getClass());
    private DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    private String template = "[%s] - %d.";
    private AtomicInteger count = new AtomicInteger();

    public String sayHelloWaitAnswer(String s) {
        log.info("Receive message {} from client", s);
        Date now = new Date();
        String answerTime = dateFormat.format(now);
        return String.format(template, answerTime, count.getAndIncrement());
    }
}
准备Spring的配置文件，因为这个示例是基于Spring Context实现的。
applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="<a href="http://www.springframework.org/schema/beans" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.springframework.org/schema/beans"
    xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.w3.org/2001/XMLSchema-instance"
    xmlns:dubbo="<a href="http://code.alibabatech.com/schema/dubbo" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://code.alibabatech.com/schema/dubbo"
    xsi:schemaLocation="http://www.springframework.org/schema/beans        http://www.springframework.org/schema/beans/spring-beans.xsd        http://code.alibabatech.com/schema/dubbo        <a href="http://code.alibabatech.com/schema/dubbo/dubbo.xsd" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

    
    <dubbo:application name="say-hello-server"  />
    
    <dubbo:registry address="zookeeper://10.10.110.58:2181" group="dubbo" client="zkclient"/>
    
    <dubbo:monitor protocol="registry"/>
    
    <dubbo:provider connections="5" accepts="8"/>

    
    <dubbo:protocol name="dubbo" port="20880"/>

    
    <dubbo:service interface="com.lefu.iexample.ISayHello" ref="simpleServer"/>

    
    <bean id="simpleServer" class="com.lefu.example.server.rpc.SayHelloImpl" />

</beans>
提供主程序入口
Main.java
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package com.lefu.example.server;
import java.io.IOException;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
    /**
     * @param args
     */
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        context.start();
        try {
            System.in.read();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

服务消费方(Consumer)

定义Maven项目，提供消费者的依赖
pom.xml
<project xmlns="<a href="http://maven.apache.org/POM/4.0.0" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://maven.apache.org/POM/4.0.0" xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 <a href="http://maven.apache.org/xsd/maven-4.0.0.xsd" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.lefu</groupId>
  <artifactId>example-client</artifactId>
  <version>1.0</version>
  <dependencies>
    <dependency>
        <groupId>com.lefu</groupId>
        <artifactId>Iexample</artifactId>
        <version>1.0</version>
    </dependency>
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>dubbo</artifactId>
      <version>2.5.3</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>3.2.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>com.github.sgroschupf</groupId>
        <artifactId>zkclient</artifactId>
        <version>0.1</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.6.4</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.6.4</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.16</version>
    </dependency>
  </dependencies>
</project>
消费者的依赖也是根据服务而定，基本上与服务提供者相同，只是不需要实现接口，只需要调用即可。
提供Spring配置文件
applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="<a href="http://www.springframework.org/schema/beans" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.springframework.org/schema/beans"
    xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://www.w3.org/2001/XMLSchema-instance"
    xmlns:dubbo="<a href="http://code.alibabatech.com/schema/dubbo" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://code.alibabatech.com/schema/dubbo"
    xsi:schemaLocation="http://www.springframework.org/schema/beans        http://www.springframework.org/schema/beans/spring-beans.xsd        http://code.alibabatech.com/schema/dubbo        <a href="http://code.alibabatech.com/schema/dubbo/dubbo.xsd" "="" style="color: rgb(50, 108, 166); text-decoration-line: none; border-radius: 0px !important; background: none !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 20px !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: auto !important;">http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

    
    <dubbo:application name="say-hello-client"  />

    <dubbo:registry address="zookeeper://10.10.110.58:2181" group="dubbo" client="zkclient"/>
    
    
    
    <dubbo:reference id="simpleClient" interface="com.lefu.iexample.ISayHello"/>

</beans>
提供Main入口调用服务
Main.java
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package com.lefu.example.client;
import java.io.IOException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.lefu.iexample.ISayHello;
public class Main {
    private final Logger log = LoggerFactory.getLogger(getClass());
    private ClassPathXmlApplicationContext context;

    public Main() {
        context = new ClassPathXmlApplicationContext("applicationContext.xml");
        context.start();
    }

    public void start() {
        ISayHello simpleClient = (ISayHello) context.getBean("simpleClient");
        for(int i = 0; i < 100; i++){
            String answer = simpleClient.sayHelloWaitAnswer("HOHO " + i);
            log.info("Answer from server {}", answer);
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        new Main().start();
        try {
            System.in.read();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
这样启动后就能正常访问服务了。

F&Q

Dubbo里很多标签在应用环境内都是唯一的，只有<dubbo:service>和<dubbo:reference>是多份的，但是需要注意，这两个标签的底层实现都是非常重的，所以尽量保证使用单例模式。
有时候在应用启动时可能使用的服务还没有注册，这个时候默认启动会报错，可以在reference标签添加check="false"来关闭启动的检测，只在真正发起调用时去检查。
Dubbo中存在很多的配置，从上往下有很多继承关系，所以默认需要的配置很少，但是越小范围的配置越高，在小范围内没有时默认采用上一级的配置，application,registry,provider,consumer都是教高层的配置，具体的配置在Dubbo官方文档中有详细的说明，大家可以去自己研究一下。
出现java.io.IOException: Can not lock the registry cache file /home/deployer/.dubbo/dubbo-registry-xxxxx.cache, ignore and retry later的问题解决方法
这个问题的出现是因为dubbo在用户目录下使用一个文件来缓存注册中心的服务提供者的信息，那么在使用前会加上文件锁，所以再一次使用这个文件是获取锁就会失败，解决的方式是：
1:确认应用内只有一个<registry>标签，不同文件的情况下，也只能有一个
2:在<registry>标签内指定一个文件，使用file属性 <registry address="xxx" file="xxx"/>
这样就能解决这个问题了

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